Embodiments of the inventive subject matter generally relate to the field of wireless communication systems, and, more specifically, to a synthesizer and modulator for use in wireless transceivers.
Wireless communication systems transfer data from a transmitting station to one or more receiving stations using modulated radio frequency (RF) signals. Bluetooth® systems are wireless communication systems governed, in part, by the Bluetooth® Special Interest Group (SIG) which publishes specifications and compliance standards. Bluetooth® devices use a communication protocol where variable length packets are sent at a particular carrier frequency (also known as hop frequency). The hop frequency varies in a pseudo-random manner from one packet to the next over 80 frequency channels with 1 MHz separation per channel. The channels span the industrial, scientific and medical (ISM) frequency range from 2.4 GHz to 2.4835 GHz including edge guard bands. Each packet is transmitted in one or more contiguous 625 us time slots, where one device is a “master” which transmits or receives in even time slots, and one or more other devices are “slaves” which send or receive in odd time slots. For a packet using the “basic rate” of 1 Mb/s, the modulation type is Gaussian frequency shift keying (GFSK). Additionally, an “enhanced data rate” mode is available, where each 1 us interval can be modulated using differential phase shift keying (DPSK) of 2 or 3 bits per symbol, thereby producing 2 or 3 Mb/s data rates. The Bluetooth® specification provides that packets which use the “enhanced data rates” utilize GFSK for a first part of the packet, and DPSK for a second part of the packet which follows shortly thereafter.